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6 - OPERATION
Outputs:
■ Compressor status message (compressor running)
■ Fault message (heat pump has a fault)
■ Message of readiness for operation (the heat pump is ready
for operation, i.e. switched on and fault-free, and may be started
at any time via remote ON/OFF)
■ Compressor running at 100 % output
■ Enables external control of a 3-way valve on the condenser
(when the 3-way valve is not switched by the heat pump)
■ Enables external control of a 3-way valve on the evaporator
(when the 3-way valve is not switched by the heat pump)
■ 0-10 V differential temperature, condenser (pump control unit)
■ 0-10 V differential temperature, evaporator (pump control unit)
6.2.3 - Control of peripherals:
In this context, peripherals are circulation pumps on the source
(evaporator) and condenser side.
Control by CARRIER heat pump:
The external source and condenser pumps can be controlled by
the heat pump controller. The required prerun and overrun times
are set by CARRIER customer service for each specific application.
The type of control is specified in the system datasheet.
Control via external building management system:
The external BMS fully regulates the targets, controls the system
peripherals (pumps, dampers, valves, etc.) and only requests
active heating or cooling from the heat pump.
In this context, the following functions must be ensured:
■ The source pump must be started approximately 1.0 minute
prior to the heat pump being enabled and must run on for around
1.0 minute after the compressor has stopped (feedback signal).
■ The condenser pump (consumption side) must start up at least
0.5 minutes before the compressor and run on for at least 0.5
minutes.
■ The compressor must not be switched more than 4 times per
hour.
■ The standard minimum operating time must not fall below 10
minutes.
To the extent required, the external BMS receives a feedback
signal about the actual operating state of the compressor by means
of a floating contact (standby, compressor running or safety shut
down). The source and condenser pumps must always run when
the compressor is working to prevent faults and damage to the
heat pump. We recommend linking the prerun and overrun timers
to the enable and feedback signals.
If the source and condenser pumps assume other functions outside
heat pump operation, it makes sense to have the external BMS
control these circulation pumps.
Control of 3-way valves by CARRIER heat pump:
The heat pump control unit can regulate the voltage supply to and
switching of the external 3-way mixing valves (actuators), both on
the source and/or condenser side. In the standard version, the
heat pump issues a 0-10 V target signal to switch the 3-way valves
on the evaporator and/or condenser side.
A 4-20 mA signal can also be provided as an option. The 3-way
valves or their actuators must be installed so that they are 100%
open to a hydraulic system on the source or consumption at a 10
V target signal. When the target signal is 0 V, the valves should
be fully open towards the bypass (short circuit circulation).
A voltage supply is provided to drive the 3-way valves. This can
be either 24 V DC (standard) or 24 V AC.
The voltage supply and type of control are defined in the system
datasheet and may vary from the standard version.
The 3-way valves used must reach an actuating time (duration
from fully open to fully closed state and vice versa) of maximum
30 seconds, 16 seconds is better.
6.2.4 - Buffer tank
The text below describes the heat pump in heating mode as an
example (target at condenser outlet), but it applies vice versa to
cooling mode (target at evaporator outlet).
Note that, depending on the hydraulic system and the temperature
spread, the heat pump target (condenser outlet) generally has to
be higher than the required temperature in the buffer tank. If for
example a temperature of 60°C is to be reached in the heating
buffer tank, the heat pump should generally be set a target value
>60°C (temperature raising).
Once the buffer tank has been heated to approximately the
required target temperature and the heat pump is off/shutting
down, the heat pump should remain off (via the remote ON/OFF)
until the buffer tank has cooled down again or the agreed
temperature spread across the condenser could be controlled
again at least over the minimum runtime.
If, for example, the target temperature for the condenser outlet is
60°C and the agreed temperature spread between condenser inlet
and condenser outlet is 10K, the heat pump should only run when
the temperature at the condenser inlet is 50°C or less.
If, for example, the target temperature for the evaporator outlet is
8°C and the agreed temperature spread between evaporator inlet
and evaporator outlet is 10K, the heat pump should only run when
the temperature at the evaporator inlet is 18°C or more.
15
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